Method and apparatus for supplementing toner in electrophotographic machines

ABSTRACT

A DEVELOPING AGENT CONSISTING OF A MAGNETIC CARRIER AND A NON-MAGNETIC TONER IS UTILIZED FOR DEVELOPING LATENT IMAGES FORMED BY AN ELECTROPHOTOGRAPHIC MACHINE. THE PERCENTAGE CONTENT OF THE TONER IN THE DEVELOPING AGENT IS DETECTED BY AN INDUCTANCE ELEMENT FOR SUPPLEMENTING THE TONER WHEREBY TO MAINTAIN AT A CONSTANT LEVEL THE PERCENTAGE CONTENT OF THE TONER CONTAINED IN THE DEVELOPING AGENT.

o 7 MASAYOSHI FURUICHI 3,698,926

METHOD AND APPARATUS FOR SUPPLEMENTING TONER IN ELECTROPHOTOGRAPHIC MACHINES Filed Nov. 10. 1970 IDETECTOR F I I CC3JNPARATOR SWITCH TONER SUPPLY MECHANISM SOURCE OF REFERENCE VOLTAGE INVENTOR MA 5A YOSl-l/ FUfiU/CH/ 5M, A M

MW l- ATTORNEYE United States Patent Ofice 3,698,926 Patented Oct. 17, 1972 US. Cl. 117-17.5 3 Claims ABSTRACT OF THE DISCLOSURE A developing agent consisting of a magnetic carrier and a non-magnetic toner is utilized for developing latent images formed by an electrophotographic machine. The percentage content of the toner in the developing agent is detected by an inductance element for supplementing the toner whereby to maintain at a constant level the percentage content of the toner contained in the developing agent.

BACKGROUND OF THE INVENTION This invention relates to apparatus for supplementing the toner in a developing agent utilized for developing latent images formed by an electrophotographic machine so as to maintain the percentage content of the toner at a predetermined level.

Electrostatic latent images formed on a photosensitive element of an electrophotographic machine are generally developed by applying a powdery developing agent consisting of a magnetic carrier and a non-magnetic toner. The toner adheres to the latent image whereas the carrier does not so that after repeated use of the developing agent the percentage content of the toner gradually decreases. For this reason, it is necessary to supplement the toner from time to time so as to maintain its percentage content in the developing agent at a predetermined constant level.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel apparatus for automatically supplementing the toner in the developing agent.

Another object of this invention is to provide a novel electrophotographic machine utilizing a developing agent always containing a toner at a constant percentage, thus producing copies of constant quality.

According to this invention there is provided apparatus for supplementing the toner in a developing agent consisting of a mixture of a toner and a magnetic carrier and utilized for developing latent images formed on a photosensitive element of an electrophotographic machine, the apparatus comprising a source of toner, a container containing the developing agent for applying the same onto the latent images, a movable impedance element which varies its impedance in accordance with the percentage content of the toner in the developing agent and means responsive to the variation in the impedance of the variable impedance element to supply the toner to the container from the source so as to maintain at a constant level the percentage content of the toner.

The impedance variation can be detected by any conventional device such as a bridge circuit and is utilized to supplement the toner.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 shows a block diagram to explain the principle of this invention; and

FIG. 2 shows a diagrammatic side view of an electrophotographic machine and a connection diagram of the novel toner supplementing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference first to FIG. 1 there is shown a block diagram showing the electric connection of essential elements of the toner supplementing device embodying the invention. The toner supplementing device comprises a detector 1 to detect the variation in the percentages of the toner contained in the developing agent for use in electrophotography to produce an electric signal, a source of reference voltage 2, and a balanced type comparator 3 for comparing the outputs from detector 1 and source 2 to produce an output voltage when the percentage of the toner decreases below a predetermined level. The output from the comparator 3 is supplied to an electromagnetic switch 6 for an electric motor 5 through an amplifier 4 for operating a toner supply mechanism 7 whenever the percentage of the toner decreases below the predetermined level.

FIG. 2 shows one example of the novel toner supplementing apparatus as applied to an electrophotographic machine 50 which may be of any conventional type. The electrophotographic machine 50 illustrated in the drawing comprises a photosensitive element including an electrode layer 9, a photoconductive layer 10 including a plurality of charge trapping levels for manifesting persistent internal polarization and a highly insulative layer 11 integrally bonded to the photoconductive layer 10. The photosensitive element is mounted on the periphery of a rotating drum 12 with the highly insulative layer faced outwardly. Around the periphery of the rotary drum 12 .are disposed a first corona discharge unit 13 to deposit a charge of one polarity on the surface of the highly insulative layer, a second cylindrical corona discharge unit 14 to deposit a charge of the opposite polarity on the surface of the highly insulative layer concurrently with the projection of a light image through the corona discharge unit 14 thus forming a latent image, a source of uniform light 15 for increasing the contrast of the latent image, and developing apparatus 8 for developing or visualizing the latent image as a powder image, and a transfer printing device wherein the powder image is transfer printed onto a recording paper 51 which is guided by guide rollers 52 to run at the same speed as the peripheral speed of the rotating drum 12. A corona discharge unit 16 may be used to assist transfer printing. There are also provided .a fourth corona discharge unit 17 which is energized by AC voltage to erase remaining latent image and a cleaner 18 including rotary brushes to remove the developing agent remaining on the surface of the photosensitive element after transfer printing.

The developing apparatus 8 comprises a casing 19 disposed to cover at least one side of the rotatary drum 12, a bucket conveyor 20 disposed in the casing to convey the powdery developing agent in the bottom thereof and to sprinkle the developing agent onto the external surface of the photosensitive element on which the latent image has been formed as above described. A rotary magnetic brush 21 is provided close to the periphery of the rotary drum 12 to collect surplus developing agent which has not adhered to the latent image.

According to this invention, a funnel of non-magnetic material 22 is disposed below magnet brush 21 to receive the powdery developing agent collected thereby. An inductance coil 23 is wound about the neck of the funnel. The reactance of the inductance coil is varied in accordance with the percentage of the toner contained in the developing agent. Inductance coil 23 is connected across the secondary winding 25 of a power transformer 24 in series with a full wave rectifier 26. A smoothing capacitor 27 and a resistor 28 are connected in parallel across the output terminals of the rectifier. Thus, inductance coil 23 and rectifier 26 constitute detector 1 and produce a voltage across resistor 28 which varies with the impedance variation of the inductance coil. A full wave rectifier 30* is connected across another secondary winding 29 of the power transformer and a smoothing capacitor 31, a resistor 32, a Zener diode 33 and a variable resistor 34- are connected in parallel across the output terminals of rectifier 30 thus producing a constant reference voltage across the variable resistor 34.

The comparator 3 comprises a bridge circuit including the resistor 28 in the detector 1, variable resistor 34 in the reference voltage generator 2 and two resistors 35 and 36. The output voltage from the bridge circuit is amplified by the amplifier 4 comprising a full wave rectifier 38 energized by a third secondary winding 37 of the power transformer 24, a resistor 39 and a smoothing capacitor 40 which are connected in parallel with the output terminals of rectifier 38, and a transistor 41. The emitter electrode of transistor 41 is connected to one output terminal of rectifier 38 through a resistor 42 whereas the collector electrode is connected to the other output electrode. The base and emitter electrodes of transistor 41 are connected across the output terminals of comparator 3. The emitter electrode of transistor 41 is also connected to the operating coil 44 of the electromagnetic switch 6 through a. transistor 43 to control motor 5.

With this arrangement, when the percentage of the toner contained in the developing agent which passes through inductance coil 23 decreases below a predetermined level, the bridge circuit of the detector 3 willbecome unbalanced and close switch 6 through transistors 41 and 44 thus operating the motor and actuating the supply mechanism 7 until the content of the toner is increased to the predetermined level.

The toner supply mechanism 7 illustrated comprises a toner reservoir 46 having a plurality of perforations 45 through its bottom and is supported on a shelf on the back of casing 19 plate valve 48 having a plurality of perforations 47 is reciprocated along the bottom of the reservoir 46 by motor 5 through a crank arm 49 to periodically align perforations 45 and 47. When these perforations are aligned the toner is supplemented to the bottom of casing 19.

As diagrammatically shown in FIG. 2 it is advantageous to make narrow the bottom opening of tunnel 22 to increase the density of the developing agent thus increasing the sensitivity. It is also advantageous to interlock a switch 50 inserted on the primary side of the power transformer 24 with the rotary drum 12 such that the switch is closed for a definite interval for each revolution of drum 12 to prevent miss operation and to increase the life of the electric components. In addition, the sieve type toner supply mechanism illustrated can be replaced by any other type supply mechanism, such as a screw conveyor, for example.

Thus, it will be clear that the invention provides a novel apparatus for automatically supplementing the toner to the developing apparatus of electrophotographic apparatus, whereby to maintain at a constant value the percentage of the toner contained in the developing-agent.

I claim:

1. In an electrophotographic copying machine, apparatus for maintaining a constant percentage of toner in a developing agent utilized for developing latent electrostatic images formed on a photosensitive element, said developing agent comprising a mixture of toner and a magnetic carrier, said apparatus comprising a source of said toner, a container for said developing agent, means for detecting the percentage of said toner in said developing agent and means responsive to said detecting means for supplying said toner to said container, the improvement comprising means for detecting the relative amount of magnetic carrier in said developing agent to indirectly determine the relative amount of toner therein, said detecting means including a funnel of nonmagnetic material disposed to receive developing agent as it falls from said photosensitive element, an inductance coil surrounding said funnel and having its inductance varied in accordance with the percentage of magnetic carrier in the developing agent, and means responsive to said inductance variation for producing an electric signal for controlling said toner supply means.

2. The improvement according to claim 1 wherein said inductance coil is included in one arm of a bridge circuit, and including a rectifier for converting said inductance variation into a variable D.C. voltage, and a source of D.C. reference voltage, said variable D.C. voltage being compared in said bridge circuit with said reference D.C. voltage to produce said electric signal.

3. In a method for maintaining a constant percentage of toner in a developing agent utilized for developing latent electrostatic images formed on a photosensitive element of an electrophotographic machine, said developing agent comprising a mixture of toner and a magnetic carrier, said method comprising the steps of storing a supply of said toner, storing said developing agent, detecting the percentage of toner in said developing agent and supplying toner to said developing agent in response to a decreased percentage of toner in the developing agent so as to maintain the percentage of said toner at a constant level, the improvement which comprises utilizing said magnetic carrier to indirectly determine and to control the amount of toner in said developing agent including the steps of providing a path for developing agent falling from aid photosensitive element, providing a magnetic-responsive element surrounding said path, transmitting an electrical signal through said element, whereby variations in said signal are produced in accordance with the relative content of magnetic material in said path, and utilizing said signal variations for controlling the supply of toner to said developing agent.

References Cited UNITED STATES PATENTS 3,376,854 4/1968 Kamola 118-637 2,671,200 3/1954 Lederer 324-71 PC 3,433,057 3/1969 Halsey 73-194 EM 2,760,769 8/1956 Onstad 73-194 EM 3,527,651 9/1970 Shellfo 118-637 X 3,376,853 4/1968 Weiler et a1. 118-637 SAMUEL S. MATTHEWS, Primary Examiner R. M. SHEER, Assistant Examiner US. Cl. X.R.

3 3 3 UNITED SIATES PATENT ()FFICE CERTIFICATE OF CORRECTION Patent No. 3, 698, 926 Dated October 17, 1972 Inventor(s) YOShl Furuichi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown. below:

Column 3, line 35, insert tonerat the end of the line,

Column 3, line 41, insert a period after "19" and --A- before "plate" Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents @3 3? UNITED S'iAiES PATENT ermcr @ERTIFICATE or comermm Patent No. 3, 698, 926 Dat d October 17, 1972 Inventor(s) Masayoshl F rulchl It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 35, insert -tonerat the end of the line,

Column 3, line 41, insert a period after "19" and -A before "plate" Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

